|Some people say we should settle gay rights disputes on the basis of the Old Testament. I say we should rely on blinking patterns.
In case you've misplaced your latest copy of Behavioral Neuroscience, there's a fascinating article about how people blink. It turns out that when males and females are exposed to a loud noise, they blink in somewhat different ways — except that lesbians appear to blink like men, not like women.The study (peer-reviewed but based on a small sample) is the latest in a growing scientific literature suggesting that sexual preferences may be not simply a matter of personal preference but part of our ingrained biology. Indeed, some geneticists believe that sexual orientation in men (though not women) may be determined in part by markers in the Xq28 chromosomal region.
One needs to be wary of these kinds of studies, partly because researchers drawn toward this field may have subconscious biases of their own. Moreover, many of the studies on the biological basis of homosexuality are flawed by small numbers or by the difficulty of finding valid random samples of gays and heterosexuals.
Still, while the data has problems, it is piling up — there are at least seven studies on twins. If there is a genetic component to homosexuality, one would expect identical twins to share sexual orientation more than fraternal twins, and that is indeed the case. An identical twin of a gay person is about twice as likely to be gay as a fraternal twin would be.
Earlier this year, the journal Personality and Individual Differences published an exhaustive review of the literature entitled "Born Gay?" After reviewing the twin studies, it concluded that 50 to 60 percent of sexual orientation might be genetic.
Many studies also suggest that sexual orientation may be linked to differences in brain anatomy. Compared with straight men, gay men appear to have a larger suprachiasmatic nucleus, a part of the brain that affects behavior, and some studies show most gay men have a larger isthmus of the corpus callosum — which may also be true of left-handed people. And that's intriguing because gays are 39 percent more likely to be left-handed than straight people.
Now look at your fingers. Men typically have a ring finger that is longer than the index finger, while in women the two are about the same length. However, two studies have suggested that lesbians have finger-length ratios that are more like those of men than of women.
Studies suggest that ring-finger length has to do with the level of androgens in the womb, and that may help explain another puzzle of homosexuality: a male is more likely to be gay if he has older brothers. It doesn't matter if he has older sisters, but for each older brother he is about 33 percent more likely to be gay. Some scientists speculate that a woman's body adjusts the androgen level in her womb as she has more sons, and that the androgens interact with genes to produce homosexuality.
O.K., these theories are potentially junk science until the studies are replicated with much larger numbers. But we also shouldn't ignore the accumulating evidence.
"There is now very strong evidence from almost two decades of `biobehavioral' research that human sexual orientation is predominantly biologically determined," said Qazi Rahman, the University of London researcher who led the blinking study. Many others don't go that far, but accept that there is probably some biological component.
Gays themselves are divided. Some welcome these studies because they confirm their own feeling that sexual orientation is more than a whim. Others fret that the implication is that homosexuals are abnormal or defective — and that future genetic screening will eliminate people like them.
For me the implication, if these studies are to believed, is different: It is that something is defective not in gays, but in discrimination against them.
A basic principle of our social covenant is that we do not discriminate against people on the basis of circumstances that they cannot choose, like race, sex and disability. If sexual orientation belongs on that list (with the caveat that the evidence is still murky), then should we still prohibit gay marriage and bar gays from serving openly in the armed forces?
Can we countenance discrimination against people for something so basic as how they blink — or whom they love?